I've been wondering that as well. Maybe he is some sort of resurrected/fallen angel and that's how he died.
I also found this when I stumbled on the painting:
Isaiah 51:9
Awake, awake, arm of the LORD, clothe yourself with strength! Awake, as in days gone by, as in generations of old. Was it not you who cut Rahab to pieces, who pierced that monster through?
I've been wondering that as well. Maybe he is some sort of resurrected/fallen angel and that's how he died.
I also found this when I stumbled on the painting:
Isaiah 51:9
Peter Mohrbacker had a lot of couple angel concepts. It's funny, you posted the exact same one I like the most. There are more on the link I posted: http://snapzu.com/ObiWanShinobi/rahab-angel-of-the-deep/